It is known that an isotropic vibrating gyro is constituted by an axially symmetrical resonator having two degrees of freedom.
The position of its vibration is identified by two electrostatic detectors, each constituted by a group of electrodes secured to the housing.
Controls for controlling the vibration are applied by two electrostatic drivers, each constituted by a group of electrodes secured to the housing.
Control of the vibration consists in compensating for damping, canceling frequency anisotropy, and possibly also modifying the orientation and/or the frequency of vibration.
In free gyro mode, the position of the vibration relative to the housing is determined in part by the angular velocity applied to the appliance. In this mode of operation, drift, i.e. the apparent rotation that results from imperfections of the appliance, depends on the position of the vibration relative to the housing.
In the frame of reference formed by the two detectors, the vibration may be characterized by its polar coordinates.
The polar angle θ is defined modulo π, and as a result the drift of the gyro is a periodic function of θ with period π.
The drift of the gyro may then be set out in the form of a Fourier series made up of terms in cos(2nθ) and sin(2nθ), where n designates the set of integers.
The main cause of mean drift (the constant term in the Fourier series) is the indexing of the detector reference points and the driver reference points.
Using the same electrodes both as drivers and as detectors serves, to a first approximation, to eliminate mean drift.
For the process to be effective, it is necessary that the mathematical expression for the detector gains and for the driver gains to be similar so that defects in the implementation of the detectors are compensated naturally by the drivers.
In known devices, the detection signal is measured by associating each detection electrode with a high impedance load circuit, i.e. with a circuit having input impedance that is very high compared with the output impedance of the corresponding detection electrode. Under such circumstances, the current delivered by the detection electrode is close to zero and the voltage picked up at the terminals of the load circuit is theoretically a linear function of the modulation of the airgap. Unfortunately, parasitic impedances resulting from defects in the fabrication of the rotation sensor degrade the linearity of the response of the sensor. In order to minimize this effect, the detection signals are generally conveyed by active shielding, which is very expensive and very bulky. Furthermore, the modulation of the electric field in the airgap gives rise to electrical losses due to impurities, thereby contributing to damping vibration in a manner that varies as a function of the orientation of the vibration, and thus to giving rise to drift that is itself a function of the orientation of the vibration relative to the housing.